Study confirms metal-on-metal hips are more likely to fail than other devicesBMJ 2012; 344 doi: https://doi.org/10.1136/bmj.e2090 (Published 14 March 2012) Cite this as: BMJ 2012;344:e2090
Metal-on-metal hip implants are far more likely to fail within five years than other types, with women at greater risk than men, a study of data from the National Joint Registry of England and Wales has shown.
The authors of the study, published in the Lancet (13 March 2012, doi:10.1016/S0140-6736(12)60353-5), call for a ban on this type of implant. Ashley Blom, of the University of Bristol, a co-author of the study, said that most people given a metal-on-metal hip had not needed to have it replaced. But with other choices available, there was no reason to take the risk. “If I were a patient I would not choose a metal-on-metal hip,” he said.
The team looked at data for 400 000 hip replacements between 2003 and 2011, of which 31 000 were metal-on-metal devices. The results show that 6.2% of metal-on-metal implants needed replacement within five years, around twice the rate recorded for other types.
Failure rates increased with larger head sizes for metal-on-metal implants, while the opposite was found for ceramic-on-ceramic implants. For younger women, many of whom were given metal-on-metal implants because it had been assumed they would last longer, the failure rate was almost four times higher than with other bearing surfaces.
The authors conclude that the evidence is unequivocal. “Metal-on-metal stemmed articulations give poor implant survival compared with other options and should not be implanted. All patients with these bearings should be carefully monitored, particularly young women implanted with large diameter heads.”
In addition to the risk of failure, metal-on-metal implants have been linked to health problems caused by metal ions in the blood and tissues (BMJ 2012;344:e1410, doi:10.1136/bmj.e1410). This issue is not dealt with in the new study, but was the subject of a warning issued at the end of February by the Medicines and Healthcare Products Regulatory Agency which said that patients with this type of implant should be carefully monitored for five years. The Lancet authors say: “We fail to see any reason for less frequent follow-up after five years since exposure to metals continues and the risk of revision does not decrease with time.”
In a commentary to accompany the study Art Sedrakyan of Weill Cornell Medical College in New York blames failures in regulation, science, and politics for this “dreadful situation” (Lancet 13 March 2012, doi:10.1016/S0140-6736(12)60372-9).
In the US, he says, there is substantial pressure from congress not to stifle innovation by excessive regulation, which has led to the availability of thousands of so called innovative hip device components compared with about 150 in the UK, and just six in Sweden. “It would not be surprising if metal-on-metal hip prostheses were just the tip of a device safety iceberg yet to be revealed,” he writes.
Metal-on-metal implants began to be used after laboratory tests suggested they would last longer. It was also assumed that larger heads should improve lubrication and reduce the danger of failure, as is the case with ceramic-on-ceramic heads. But experience has proved both these assumptions false. Professor Blom said that the rate of failure the team found for metal hips was likely to be an underestimate, since not all patients report problems or have surgery to put them right.
Cite this as: BMJ 2012;344:e2090